@Petulant_Radish: Drive on to the first ball, roll just over the midway point then gently tap reverse intermittently, it'll spin the ball forwards and you can ride it to the next ball. Getting on to that can be a PITA though. Whatever you do though - stay really close to the top of the first ball - it's very easy to slip a little too far down and then you can't get back up again, and you'll end up wedged between the balls.